Uranus seen from Titania, illustration. From the night-time surface of Titania, the crescent discs of Uranus and its three innermost large moons glow steadily overhead. Though the planet appears about 13 times larger than our Moon does from Earth it shines as bright as only two full Moons, so feeble is the sunlight.

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Illustration of the Earth, Moon and Sun showing a passing comet. Cities are seen glistening, defining the edges of the Earth's continents. Comets are balls of loosely packed 'dirty ice'. As they near the Sun, their gases sublimate and form long tails blustering away from the star. The tails can stretch for tens of thousands of kilometres, dwarfing even the Earth-Moon separation.

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The Earth and Moon seen from space, illustration.

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The Earth seen from space, illustration.

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Illustration of a comet passing the innermost planet, Mercury, and approaching the Sun.

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Illustration of a free-floating planet. These planets are odd in that, unlike most extrasolar objects, they do not seem to be in orbit around a star - they are free-floating planets drifting between the stars and galaxies. Free floating planets such as these may result from being ejected from a protoplanetary disc due to gravitational perturbations from other massive objects. This planet has cloud bands like those of the gas giant Jupiter.

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Illustration of a free-floating planet. These planets are odd in that, unlike most extrasolar objects, they do not seem to be in orbit around a star - they are free-floating planets drifting between the stars and galaxies. Free floating planets such as these may result from being ejected from a protoplanetary disc due to gravitational perturbations from other massive objects. This planet has cloud bands like those of the gas giant Jupiter.

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Conceptual illustration of a space station, terminal or habitat in Earth orbit in the future. People are seen pointing outside, and one of them is using a telescope.

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Illustration of the Universe's first generations of stars. Scientists estimate that the first stars began to shine when the Universe was just 180 million years old, a fraction of its 13.8-billion-year age. Astronomers have detected these stars indirectly for the first time, by observing the signals in hydrogen gas that these stars illuminated. These stars are theorized to have been very massive, burning through their hydrogen supplies in around a million years or so, and then turning into the red giants and supergiants seen in this illustration.

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Illustration of a sungrazing comet. These are comets that pass very close to the Sun at perihelion. Sometimes they can skirt above the photosphere at distances of just a few thousand kilometres - the mere diameter of a small planet. Occasionally comets are completely evaporated in this process, but some can last several passes before either falling into the Sun or disintegrating because of tidal forces.

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Illustration of a free-floating planet in front of a lenticular galaxy. These planets are odd in that, unlike most extrasolar objects, they do not seem to be in orbit around a star - they are free-floating planets drifting between the stars and galaxies. Free floating planets such as these may result from being ejected from a protoplanetary disc due to gravitational perturbations from other massive objects. This planet has cloud bands like those of the gas giant Jupiter.

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Illustration of a Voyager probe at the Oort cloud. The two Voyager probes were launched in late 1970s. Voyager 1 has now passed into interstellar space - beyond the influence of the Sun's magnetic field - and Voyager 2 is set to do so in the early 2020s. Some 300 years from now, the probes will enter the beginnings of the Oort cloud - a swarm of inert comet nuclei surrounding the Sun up to perhaps 50,000 astronomical units from it. The cloud is so vast that the probes are expected to take around 40,000 years to pass through it into clear space.